Rapamycin is a new drug that is in the first phase of clinical testing. It is hoped that some day rapamycin will be used to prevent kidney transplant rejection. Rapamycin blood levels will be measured in this study to determine the relationship between rapamycin dose levels and blood levels. The research question is: does doubling the dose double the blood level? It is important to determine this relationship because blood levels do not always correspond to the dose a patient takes.